Electronic whiteboards that enable a user to interact with a projected image by engaging a screen displaying the image with an object are known. Conventional systems suffer from various drawbacks. For example, in general these systems are not capable of simultaneously accepting inputs from a plurality of objects. Or, if a plurality of objects are being used to provide inputs to the system, a conventional system may not be capable of identifying the different objects being used. Systems typically do not enable a user to interact with the project image via an object that emits electromagnetic radiation (e.g., a light pen) and an object that is passive optically (e.g., reflects and/or scatters radiation, but does not emit). Additionally, current interactive display systems may be costly, temperamental, bulky, slow, or otherwise in efficient. Other drawbacks also exist.